1. Field of the Invention
The present invention relates to network technology. More particularly, the present invention relates to maintaining high availability of network devices.
2. Description of the Related Art
In most enterprise networks, a tiered network design is employed, with redundant network devices at various tiers. A typical network design is illustrated in FIG. 1. Core layer 105 may be connected to data center 110 and/or Internet 115. Core layer 105 generally includes 2 switches, each of which is connected with each device in distribution layer 120 for redundancy purposes. (As used herein the term “switch” will be used to mean an actual switch, a router, or any similar network device.) Similarly, each device in wiring closet/access layer 125 is normally connected to two devices of distribution layer 120.
The pairs of switches in the distribution and core layers normally act as peer devices. Typically, network traffic is load balanced between the peers. If one of the peers fails, then all traffic is re-directed to the other switch.
Within switches configured for high availability, there is an “active” supervisor and a “standby” supervisor. The active supervisor is responsible for routing network traffic on the network and maintaining the appropriate routing tables, port index tables, etc. The running configuration file of the active supervisor is typically modified during the operation of the active supervisor. The standby supervisor is available in the event of the failure of the active supervisor.
Merely connecting the active and standby supervisors is not sufficient to allow the standby supervisor to take over the functions of the active supervisor in the event the active supervisor fails. The supervisors must be configured to allow a “switchover” to take place, preferably without causing much (if any) disruption of the network. Examples of some methods and devices for achieving such “high availability” are described, for example, in U.S. patent application Ser. No. 10/156,563, filed May 24, 2002, which is hereby incorporated by reference for all purposes.
In general, the standby supervisor may be configured in a “cold,” “warm” or “hot” standby state. Although these terms are not precisely defined, an increase in figurative temperature indicates a relatively higher state of readiness of the standby supervisor. In other words, a standby supervisor operating in a warm state will be able to take over the functions of the active supervisor more quickly than a standby supervisor operating in a cold state. A standby supervisor operating in a warm state may, for example, have its configuration state continuously synchronized to match the running configuration of the active supervisor. A standby supervisor operating in a hot state may, for example, also have its routing tables, port index tables, etc., continuously synchronized to match those of the active supervisor.
Recently, the present assignee has developed methods and devices to form networks that preserve the robust qualities of a conventional network topology, but which are simpler to manage. However, these novel configurations introduce configurations to which former methods of maintaining high availability do not apply. It would be desirable to implement improved mechanisms for maintaining high availability in such networks.